Block access storage devices typically store blocks of data on a selected physical media. Disc drive interfaces typically use fixed-length logical block sizes, such as a size of 512 bytes. These types of interfaces may be used by disc drives, solid-state drives, hybrid (disc and solid-state) drives, and other storage devices. Tape drive interfaces use fixed or variable length logical block sizes. The logical blocks may be compressed, as is common in tape drives. Meanwhile, encoding methods or redundant information, such as error-correcting codes, may add to the information recorded for a logical block. Block access storage devices typically transform the logical blocks received from the host to different logical blocks to be stored by encoding, adding redundancy, grouping and/or compressing. The transformed logical blocks typically have a transformed logical block address that is a transformation of the logical block address used at the host interface.
The atomic unit of write access in a block access storage device is a physical block. The physical media may support variable physical block lengths, as with common tape formats. More typically, the media has a fixed-length physical block size. Disc drive design usually matches the physical block size to the logical block size plus the size of the added information. Some designs have larger physical blocks that accommodate an integral number of logical blocks. Flash designs typically include physical blocks called pages that have space for a number of logical blocks plus a certain amount of added information.